1. Technical Field of the Invention
The present invention relates to an emergency brake mechanism and, particularly, to a centrifugal emergency brake mechanism.
2. Description of the Prior Art
In a generally known centrifugal emergency brake mechanism, brake shoes are pivotally supported to a rotation axis at one end thereof, so that when the rotation axis is rotated, the brake shoes are centrifuged and swung outward. Thus, part of the spread-out brake shoes are brought into press-contact with a fixed surface, so as to apply friction to the rotation axis and apply braking force.
In this conventional centrifugal emergency brake mechanism, since the frictional force for the brake is generated by the centrifugal force generated by the mass of the brake shoes rotated, generation of a strong frictional force requires an increase in the mass of the brake shoes or in the rotation speed of the brake shoes.
When an increased frictional force is produced by increasing the mass of the brake shoes, there arises a problem in that the brake shoes and thus the entire emergency brake mechanism are increased in size. As a result, the brake shoes are not suitable for installation on a compact brake mechanism.
On the other hand, when an increased centrifugal force is produced by increasing the rotation speed of the brake shoes, there arises a problem in that it is practically infeasible to mount the emergency brake mechanism on a rotation axis having a relatively low revolution (rotation speed), such as the rotation axis of a shutter used in a factory, warehouse and the like, or a rope winding shaft of a lift and the like on and from which an escape rope is wound and paid out.
If a heavyweight shutter is used for a factory or warehouse and is pulled down, the rotation axis gradually increases in rotation speed as the shutter paid out increases in length and in downward inertia force. As a result of this, when the bottom end of the shutter gets down to the ground, a large impact and noises are produced, and also one""s fingers or toes might be caught in or pinched between the shutter and the ground and injured or cut off. In an escape lift having a gondola, for example, if the rotation axis of the escape lift gradually increases in rotation speed, the gondola is put in danger when landed.
In the light of the problems above, the present invention has been proposed. It is the object of the present invention to provide a centrifugal emergency brake mechanism having a compact size that is applicable to a variety of devices and can produce an excellent braking power for the compact size.
In order to accomplish the object mentioned above, an emergency brake mechanism according to the present invention comprises a planetary set-up mechanism provided between a rotation input shaft and a fixed portion; weights; and brake shoes. The brake shoes are arranged on the rotation input shaft so as to be in association with it, and the weights are centrifuged by an increased rotation speed produced by the planetary set-up gear. Through the action of the centrifugal force of the weights, friction surfaces of the brake shoes are brought into press-contact with the fixed portion, to reduce rotation of the rotation input shaft.
In the emergency brake mechanism mentioned above, frictional contact portions are formed in the brake shoes at portions thereof on the drive shaft side, so as to directly or indirectly contact the drive shaft. In addition, the portions of the brake shoes with which the frictional contact are brought into contact are formed as slant locking surfaces.
In the emergency brake mechanism mentioned above, the rotation input shaft may be shaft of a shutter and may be structured so as to control a lowering speed of the shutter.